What Is Glass Wool Used For?

Glass wool (originally known also as fiberglass) is an insulating material made from fibers of glass arranged using a binder into a texture similar to wool.

Glass Wool

Glass wool - thermal insulation glass wool (originally known also as fiberglass) is an insulating material made from fibers of glass arranged using a binder into a texture similar to wool. Glass wool and stone wool is produced from mineral fibers and are therefore often referred to as ‘mineral wools’. Mineral wool is a general name for fiber materials that are formed by spinning or drawing molten minerals. Glass wool is a furnace product of molten glass at a temperature of about 1450 °C. 

From the melted glass, fibers are spun. This process is based on spinning molten glass in high-speed spinning heads somewhat like the process used to produce cotton candy. During the spinning of the glass fibers, a binding agent is injected. Glass wool is then produced in rolls or in slabs, with different thermal and mechanical properties. It may also be produced as a material that can be sprayed or applied in place, on the surface to be insulated.

 Centrifugal Glass Wool 

Applications of glass wool include structural insulation, pipe insulation, filtration, and soundproofing. Glass wool is a versatile material that can be used for the insulation of walls, roofs, and floors. It can be a loose-fill material, blown into attics, or, together with an active binder sprayed on the underside of structures. During the installation of the glass wool, it should be kept dry at all times, since an increase of the moisture content causes a significant increase in thermal conductivity.

Thermal Conductivity of Glass Wool

Thermal Insulators - ParametersThermal conductivity is defined as the amount of heat (in watts) transferred through a square area of material of a given thickness (in meters) due to a difference in temperature. The lower the thermal conductivity of the material the greater the material’s ability to resist heat transfer, and hence the greater the insulation’s effectiveness. Typical thermal conductivity values for glass wools are between 0.023 and 0.040W/m∙K.

In general, thermal insulation is primarily based on the very low thermal conductivity of gases. Gases possess poor thermal conduction properties compared to liquids and solids, and thus make a good insulation material if they can be trapped (e.g. in a foam-like structure). Air and other gases are generally good insulators. But the main benefit is in the absence of convection. Therefore, many insulating materials (e.g. glass wool) function simply by having a large number of gas-filled pockets which prevent large-scale convection.

Alternation of gas pocket and solid material causes the heat must be transferred through many interfaces causing a rapid decrease in heat transfer coefficient.

Foil-Clad Glass Wool

Example – Glass Wool Insulation

heat loss through the wall - example - calculation major source of heat loss from a house is through walls. Calculate the rate of heat flux through a wall 3 m x 10 m in the area (A = 30 m2). The wall is 15 cm thick (L1) and it is made of bricks with the thermal conductivity of k1 = 1.0 W/m.K (poor thermal insulator). Assume that, the indoor and the outdoor temperatures are 22°C and -8°C, and the convection heat transfer coefficients on the inner and the outer sides are h1 = 10 W/m2K and h2 = 30 W/m2K, respectively. Note that, these convection coefficients strongly depend especially on ambient and interior conditions (wind, humidity, etc.).

Calculate the heat flux (heat loss) through this non-insulated wall.

Now assume thermal insulation on the outer side of this wall. Use glass wool insulation 10 cm thick (L2) with the thermal conductivity of k2 = 0.023 W/m.K and calculate the heat flux (heat loss) through this composite wall.

Solution:

As was written, many of the heat transfer processes involve composite systems and even involve a combination of both conduction and convection. With these composite systems, it is often convenient to work with an overall heat transfer coefficient, known as a U-factor.